1. Field of the Invention
This invention relates to a spectrally sensitized photographic gelatino-silver halide emulsion and more particularly, it is concerned with a photographic silver halide emulsion suitable for use as a color sensitive material, in which the green sensitivity is raised by the combined use of at least two sensitizing dyes.
2. Description of the Prior Art
In the production of light-sensitive materials, as is well known, the spectral sensitizing technique is very important and essential for the production of color light-sensitive materials. Of the blue-sensitive, green-sensitive and red-sensitive silver halide photographic emulsions which compose a color light-sensitive material, the property of the green-sensitive silver halide emulsion affects markedly the quality of a color photograph. That is to say, a slight difference of the green sensitivities or the distribution of spectral sensitivity in the green region affects markedly the color reproduction of a color light-sensitive material and the quality of a color image. Therefore, the spectral sensitization of green region is a problem in which those working in light-sensitive materials make detailed studies with care.
It is known that the spectral sensitization of a light-sensitive material is affected by various properties of a silver halide emulsion used; for example, the crystal habit of the silver halide, the grain size, the halogen composition, its chemical sensitization, its pH and the concentration of silver ion, by the kinds of binders and additives such as antifoggants, stabilizers and coating agents and, in the case of the color material, of the incorporated type, by a coupler, a coupler dispersing agent, a plasticizer, a hardener and dyestuffs for photography. These are inclined to act so as dyes weaken the spectral sensitization. The spectral sensitivity of a light-sensitive material depends largely on not only the chemical structure of the sensitizing dye used but the addition method to an emulsion used. Sensitizing dyes are used alone in some cases, buut, in many cases, two or more sensitizing dyes are used in combination in order to obtain a suitable distribution of spectral sensitivity. The spectral sensitivity obtained when dyess are used in combination is ordinarily not higher than the maximum spectral sensitivity obtained when the dyes are used alone. However, in a particular case of using certain sensitizing dyes in combination, a higher spectral sensitivity can be superadditively obtained. This is called supersensitization. It is also known that combinations of two or more sensitizing dyes to give this supersensitization are so selective with each other that it is very difficult to estimate their actions from the difference of the apparent chemical structures.
The supersensitizing technique for color light-sensitive materials in the green region has been studied by many researchers. However, the prior art has many disadvantages.